Tripoli: Libyan rebels claimed to be in control of most of the Libyan capital on Monday after their lightning advance on Tripoli heralded the fall of Muammar Gaddafi's nearly 42-year regime, but scattered battles erupted and the mercurial leader's whereabouts remained unknown.

The international community called on Gaddafi to step down and moved ahead with post-war planning as euphoric residents celebrated in the Green Square, the symbolic heart of the Gaddafi regime, but colleagues warned he wouldn't go easily.

NATO promised to continue airstrikes until all pro- Gaddafi forces surrender or return to barracks.

The relative ease with which the rebels captured Tripoli in an hours-long blitz backed by NATO airstrikes showcased the evolution of the opposition fighters who first rose against the regime six months ago, swiftly capturing the eastern part of the vast North African nation but failing to muster enough punch to advance westward toward Tripoli even with the help of months of NATO airstrikes.

For months, the rebels were judged to be big on zeal but short on organization and discipline, but their stunning success in Tripoli showed a high level of planning, coordination and discipline.

In London, British Prime Minister David Cameron said frozen Libyan assets would soon be released to help the country's rebels establish order, saying Gaddafi's regime was "falling apart and in full retreat."

Rebel spokesman Mohammed Abdel-Rahman, who was in Tripoli, cautioned that pockets of resistance remained and that as long as Gaddafi remains on the run the "danger is still there."

Clashes broke out early on Monday at Gaddafi’s longtime command center known as Bab al-Aziziya when Government tanks emerged from the complex and opened fire at rebels trying to get in, according to Abdel-Rahman and a neighbor.

Tripoli resident Moammar al-Warfali, whose family home is next to the compound, said there appeared to be only a few tanks belonging to the remaining Gadhafi forces that have not fled or surrendered.

"When I climb the stairs and look at it from the roof, I see nothing at Bab al-Aziziya," he said. "NATO has demolished it all and nothing remains."

The Rixos also remained under the control of Gaddafi forces, with two trucks loaded with anti-aircraft machine guns and pro-regime fighters and snipers posted behind trees.

Rebels and Tripoli residents set up checkpoints elsewhere in the city.

The rebels' top diplomat in London, Mahmud Nacua, said clashes were continuing in Tripoli, but opposition forces controlled 95 percent of the city. He vowed Gaddafi would be found, saying "the fighters will turn over every stone to find him" and make sure he faced justice.

A rebel field commander said reinforcements were arriving at Tripoli by sea from the north as well as the south and the Southeast.

"Our fighters are coming from all directions and, God willing, today we will liberate the whole city," the commander, Suleiman Sifaw, told a news agency.

Opposition fighters captured his son and one-time heir apparent, Seif al-Islam, who along with his father faces charges of crimes against humanity at the International Criminal Court in the Netherlands. Another son was under house arrest.

Rebel chief Mustafa Abdel-Jalil vowed on Monday to give Gaddafi a "fair trial with all legal guarantees" when captured.

"It's over, frizz-head," chanted hundreds of jubilant men and women massed in Green Square late on Sunday, using a mocking nickname of the curly-haired Gaddafi. The revelers fired shots in the air, clapped and waved the rebels' tricolor flag. Some set fire to the green flag of Gaddafi’s regime and shot holes in a poster with the leader's image.

But Gaddafi's defiance in a series of angry audio messages raised the possibility of a last-ditch fight over the capital, home to 2 million people. Gaddafi, who was not shown in the messages, called on his supporters to march in the streets of the capital and "purify it" of "the rats."

Government Spokesman Moussa Ibrahim also claimed the regime has "thousands and thousands of fighters" and vowed, "We will fight. We have whole cities on our sides. They are coming en mass to protect Tripoli to join the fight." Gaddafi’s former right-hand man, who defected last week to Italy, said the longtime leader would not go easily.

"I think it's impossible that he'll surrender," Abdel-Salam Jalloud told reporters, adding that "He doesn't have the courage, like Hitler, to kill himself." Gaddafi may have fled to Algeria

Muammar Gaddafi, who has ruled Libya uninterrupted for 42 years remained elusive as rebel forces swept into his capital Tripoli with reports suggesting that the dictator had fled to neighbouring Algeria or could be holed-up in a bunker to attempt a last stand.

With rebels reported in occupation of 95 percent of the capital except Gaddafi's command and control centre Bab al-Aziziya, speculation was rife about the whereabouts of Gaddafi.

A rebel spokesman claimed that Gaddafi and some of his family members were spotted making a dash towards Algeria, while news channel in the Libyan capital said that Gaddafi was in the Tajura-Cardiac hospital. But said there were no reports on whether Gaddafi was undergoing treatment in the hospital or simply taking refuge.

Media house reported that the Libyan strongman was in Tripoli in his Bab al-Aziziya command and control centre.

The Bab al-Aziziya compound has been regularly pounded by NATO airstrikes and most of the buildings in the compound have been flattened.

Rebel sources said that Gaddafi had constructed a number of deep bunkers in the complex where he could take cover.

But the rebels vowed that "Gaddafi would be hunted down". "We will leave no stone unturned to trace the tyrant and make him face trial," rebels commander told a news channel.

While there was a big question mark about Gaddafi, news channel reported that his all powerful brother-in-law and intelligence chief Abdullah Senussi had been killed.

Al-jazeera also said that Gaddafi's favourite son Saif al-Islam, who along with his father faces charges of crimes against humanity at the International Criminal Court in the Netherlands had been captured and was safe.

Another news channel reported that two other sons of Gaddafi, Mohammad and Saadi, have been captured.

Mohammad Gaddafi was captured in dramatic circumstances while giving an interview to a news channel. (Agencies)